Content delivery network is a network architecture build on the existing internet. Hot web resources, such as web pages, images, music and videos, that are frequently required by the users are distributed to edges nodes closest to the users. In this way, the users could download the web resources quickly. Thus, network congestion is reduced, and the response rate of web sites is also improved.
However, the web resources are growing rapidly, and the storage space of the CDN is limited. Therefore, the files stored in the CDN should be cleaned periodically. As the number of files is huge, a lot of time is consumed to clean the files. It is desirable to provide an efficient way to clean the files.